In the semiconductor manufacturing steps, various processing treatments are performed to obtain desired device structures such as film-forming processing by PVD method, CVD method, or the like, as well as ion implantation processing, heating processing, etching processing, or the like. In a vacuum processing apparatus to perform these processing treatments, there is disposed a so-called electrostatic chuck in order to hold in position a silicon wafer (hereinafter, simply referred to as “wafer”) as a substrate to be processed in the processing chamber. As the electrostatic chuck, there is conventionally known in Patent Document 1 a so-called bipolar electrostatic chuck which has mounted a chuck plate of a dielectric material on an upper surface of the chuck main body into which positive and negative electrodes are buried.
Depending on the processing to be performed in the vacuum processing apparatus, there are cases where the wafer is heated to a predetermined temperature. In such a case, it is known that the chuck main body has assembled therein, e.g., a resistance heating type of heating means, and that there is formed a rib portion which comes into surface contact with a peripheral edge portion on a rear surface of the wafer (i.e., the side opposite to the surface on which the predetermined processing is performed). In an inner space enclosed by this rib portion, a plurality of supporting portions are vertically disposed, e.g., in a coaxial manner to thereby constitute a chuck plate. At the time of heating and cooling of the wafer, inert gas such as Ar gas or the like is supplied to the inner space through a gas passage which is formed in the chuck main body. By thus forming an inert gas atmosphere in the inner space to be defined by the rib portion and the rear surface of the wafer, the heat transmission to the wafer is assisted to efficiently heat or cool the wafer.
By the way, in the electrostatic chuck having the above-mentioned constitution, at the time of heating and cooling the wafer, the rib portion and the supporting portion of the chuck plate will get rubbed by the wafer and gradually wear out due to the difference in thermal expansion between the wafer and the electrostatic chuck. As a solution, like in the above-mentioned Patent Document 1, it has so far been practiced to: cause to flow AC current through the capacitance of the chuck plate from an AC power supply to thereby monitor the current value. By thereby judging the limit of use as quickly as possible, the damage to the wafer in the processing chamber due to poor attraction of the wafer or the like can thus be prevented, thereby improving the productivity.
On the other hand, in order to further improve the productivity, there is recently a tendency to use wafers of larger diameter and thinner plate thickness (thickness below 700 μm). This kind of wafers gives rise to warping in various directions due to predetermined processing treatments. In addition, during any of the processing treatments, the state of warping of the wafer will vary due to heating and cooling of the wafer. Therefore, there are cases where wafers get damaged, not only during processing treatment, but also during the time when the warped wafer is held by the electrostatic chuck or when the wafer is transported by releasing the attraction of the wafer. As a result, there is a disadvantage in that only judging the limit of use of the electrostatic chuck cannot improve the productivity while attaining, at the same time, the improvement in the yield of the product. It therefore becomes important how best the wafer state is to be managed.